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June 15, 2006
"I was drinkin so much I forgot what life was about. Gold! Beautiful gold! Nuggets as big as your fists!"
In the spirit of "if something's worth doing, it's worth doing well," a college professor has cobbled together directions for how to cheat good.
There's gold under that thar mantle! The center of the earth has a high concentration of Au. Strangely, the story also puts a modern twist on the way the ancients thought planets influenced the growth of metals in the earth: via
"By looking at other stars that are currently at the state our Sun was in then, we can see that they are surrounded by a flattened disc of dust and gas," Wood says.
"We know that within about 10,000 years these formed into small bodies that were about 10 kilometres across."
Radioactive dating has shown that over the next 100,000 to one million years, those small "planetesimals" collided to form Moon-to-Mars sized planetary embryos.
Early in its history, the Earth was probably covered in a sea of molten rock, hundreds of kilometres deep.
During the planet's development, this "magma ocean" reacted with metals in the planetesimals, extracting many of the most important and interesting elements, including gold, and eventually depositing them in the Earth's own iron-rich core.
To calculate how much gold was in the Earth's core Wood compared the composition of the Earth's crust with that of meteorites, which can be used to represent planetesimals.
He and other researchers have found that the meteorites had similar levels of all elements that would not normally dissolve in iron.
But they also noted that meteorites had higher levels of elements such as gold, platinum and nickel.
"This tells us that the Earth is chemically very similar to those meteorites, but the Earth's crust is depleted in all those elements that like to dissolve in iron," Wood says.
There's only one place those elements can have gone - the molten core.
Posted by Jon Rubin at June 15, 2006 10:19 PM
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